text:
When departing IFR, when do I switch from Tower to Departure?
When departing IFR from a Class D airport, must you wait until the Tower instructs you to change to Departure?

Are you asking about a specific country/regulator, or is this a general question?

You should never leave a control frequency without an explicit instruction to do so. This can be a literal instruction (the controller telling you to contact another unit/frequency), or a procedure described in the AIP. For example, at some airports, a part of the description of the standard instrument departures read "When passing 1000 ft, contact Departure on 124.975" or similar. Here is an example from Copenhagen, Denmark:

Unless such a procedure is in place, you wait until the tower changes you to the next frequency. That's the beauty of flying as a controlled flight - you don't need to worry about which frequency you should be on, the current controller will always hand you over to the next one when required.

"KASTRUP DEPARTURE". I read that as Ketsup Departure. I must be hungry

Since you are IFR, in your question, you do as told.  Which means as instructed or as cleared.  If a SID is applicable, you conform to the SID, unless cleared otherwise.
If you are VFR, which you said you were not, then the game is different. In general the do as instructed / cleared applies, but some new nuances come into play.
For example, VFR, you need only maintain tower com while in Class D, so leaving Class D, you can go where you want.  May not be considered polite, but if you think you are forgotten, and they are really busy, you might just go.  They will see that you checked in with departure at most facilities.
Common courtesy is to let the tower hand you off, or prompt them for a hand off.

Please don't just leave the frequency without telling. We don't just forget aircraft. If you leave and we later try to call you, it might get treated as a radio failure.

@j.hougaard I have certainly had ATC forget me when operating VFR. Moreover VFR lost comm after exiting ATC's airspace is a non-issue in the US.

Like @JonathanWalters I have had ATC (tower as well as approach, departure, and center, forget about me VFR, and have also had it happen IFR, although rarely.  In the distant past, it was common for places I flew IFR to not have constant VHF/UHF communication in CONUS.  Also, it was quite common that I would do approaches in uncontrolled airspace, where IFR communications were not always available, and were not essential.

@J.Hougaard, if you're VFR at KFRG, they never give any hand-off. It's a very busy delta, and they just want you to go on your way. I typically remain on frequency for a few miles outside the delta, then switch. I've definitely seen other east coast deltas work this way.

That's pretty much standard fare, unless you are in some low volume area like Ithaca NY Class D.  Except on move-in day at the college.  Then it's hard to find ramp space for your 604.

Yes, no frequency changes until instructed.
(unless previously requested and approved, which seems unlikely on an IFR departure)
The phrase is typically, "N12345, Over to Departure. G'day"


text:
What does the phrase from the FAA, "clear to maneuver" mean?
What, if anything, does the phrase, "clear to maneuver" mean if given by an FAA airspace controller?

Is this from an airshow?

As far as I can tell, is not standard terminology,  can you give context?  Since is not standard, (and even if it was) you are more than welcome to ask the controller directly for clarification. In any case it doesn't relieve the pilot from "see and avoid".

It seems Cleared to maneuver can be found in military / flight test ATC instructions. See bottom of page 9. Also mentioned here about Concorde accident in 2000, in an emergency context.

That isn't standard FAA phraseology; at least, it isn't anywhere in the ATC orders. The closest thing is in section 9-2-20 on evasive action maneuvers. I know nothing about them, but they seem to be a military training thing:

PHRASEOLOGY−
  CLEARED TO CONDUCT EVASIVE ACTION MANEUVER FROM (fix) TO
  (fix),
  and
  (number of miles) EITHER SIDE OF CENTERLINE,
  and
  MAINTAIN
  (altitude) THROUGH (altitude),
  and
  COMPLETE MANEUVER AT (fix) AT
  (altitude)

But of course both pilots and controllers use non-standard phraseology all the time, especially for unusual situations. It's certainly possible that a controller somewhere has indeed said "cleared to maneuver as requested" or something similar. Although the 'correct' phraseology would be "approved as requested" (see section 2-1-18 of the orders) for a general request.
Another possibility is that it's military phraseology, not civilian. If you can link to a source or ATC recording then you might get a better answer.

It means, on the radar and from other information report available to the controller, it appears that no aircraft are in the way, and that the maneuver can be performed in time. No other aircraft appear to be coming in the area needed to perform the maneuver, in the time that the maneuver need to be performed. It also implies that the controller is aware and ready to respond in case of emergency.

Citation please.

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text:
What high-lift devices are used on the Bombardier Dash 8 Q400?
What type of flaps, slats or other high-lift devices are used on this aircraft?

I won't post as an answer as I don't have references to hand - but essentially: No slats, and single slotted flaps.

The Dash8 - Q400 - Aeroplane General PDF (courtesy of smartcockpit.com) indicates on page 27 that there are inboard and outboard flaps.
Reading through the Dash8 - Q400 Flight Controls PDF (also from smartcockpit.com) indicates that:

Two single-slotted inboard and outboard fowler flaps are attached to the trailling edge of each wing (Figure 12.8-1).page 43

There is no indication of slats or any other high-lift device.

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text:
How is MEF calculated for Canadian VNC?
According to the VNC, the MEF represents the highest feature in each quadrangle. It refers to

AIM RAC 5.4 and CAR 602.15(2b) which basically says "lower than 500 AGL (CAR 602.14(2b)) ok, when for aerial application or aerial inspection, photography, ..."
AIM AIR 1.5 which is about "Pressure Altitude" which I guess is because the heights are ASL

Now, the sample quadrangle here shows a MEF of 2700'. Looking at that quadrangle, the highest obstacle I would say is the mountain in the very east, north of 50°35' which is 2290' high. I wonder where that difference comes from.
I think that both figures, 2700' MEF and 2290' are ASL. Therefore it can't be the difference between ASL and AGL.
It always seems to be ~400' more than the highest feature.

Not sure about Canada but In the US the MEF's are set by taking the highest obstacle in the quad, adding 100ft (for man made objects) or 300 feet (for natural obstructions such as trees) then rounding up to the next 100ft. So under US charting rules it would most likely be 2600 ft. Canada must add an extra 100 ft. And remember that obstacles less than a certain height AGL (200 ft in the US) may not be charted, but if they're the highest object they will still affect the MEF. So if there's a 100 ft tree on top of that mountain that would add to the high point.

According to Aeronautical Information Circular 26/11 VFR Navigation Charts—Clarification of the Maximum Elevation Figure the

The MEF is calculated by taking the higher value of:

the top elevation of the highest obstacle plus the vertical accuracy (variable) of the terrain
  source data; or
the elevation of the highest terrain plus 328 feet plus vertical accuracy of the terrain source
  data.

So the 2700' could come from 2290' plus 328' rounded up to next hundred feet.


text:
Do the DO-178 standards include guidelines on cyclomatic complexity?
Is there any guideline related to the cyclomatic complexity of software that complies with the DO-178C or DO-178B standards?

Short answer is No.
From the note after 5.2.2.g

The current state of software engineering does not permit a quantitative
  correlation between complexity and the attainment of system safety objectives.
  While no objective guidance can be provided, the software design process should
  avoid introducing complexity because as the complexity of software increases, it
  becomes more difficult to verify the design and to show that the safety-related
  requirements are satisfied.

DO-178C is focused on defining process objectives rather than design guidelines.  Your process (specifically Design Standards) might specify a certain maximum complexity value, but it wouldn't be driven directly from DO-178C

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text:
Does DO-178C require static code analysis for level A software?
Does DO-178C have any guidelines on using static code analysis for level A software?
As per Do-178C:

Section 6.3   Software Reviews and Analyses
  Reviews and analyses are applied to the outputs of the software development processes. One distinction between reviews and analyses is that analyses provide repeatable evidence of correctness and reviews provide a qualitative assessment of correctness. A review may consist of an inspection of an output of a process guided by a checklist or similar aid.
An analysis may examine in detail the functionality, performance,
  traceability, and safety implications of a software component, and its
  relationship to other components within the system or equipment

Can this achieved by Static analysis ? Some of the tools like polyspace which has misra standard checks

This is a software question, doesn't fall within the scope of this site. https://stackoverflow.com/ is a better place to ask this.

While the question does pertain to software, this question is really targeting the certification of software in avionics, which is on topic here.

What DO-178 objective are you hoping to meet using static code analysis? Are you looking to take credit for using static code analysis in some fashion?

I agree with @selectstriker2.  This question is primarily about  how DO-178C works and less about static analysis itself. You could replace static analysis with formal methods or even integration testing and the answer would be mostly the same.

DO-178C is a means of compliance, so it sets out what you need to do to show you are meeting your required safety levels in your design.  It does not give advice on what methods you might use along the way.
I have seen static analysis used as part of the process, often with hardware integration and system testing.
DO-178 tools need to be qualified for DO-178 if you are using them to test your software.  I am not aware of anyone successfully using tools qualified for other standards (e.g. MISRA) in avionics.

Static Analysis is usually used in the SDP and SVP as a means of enforcing coding standards and conventions, as well as part of the effort to ensure that the code is IEEE 754/C99 (or whatever you stated) compliant. This is usually a means to cut down on review findings, increase code quality, and ease verification by inspection.

Welcome to Av.SE. I'm not sure that this answers the stated question.

You're right. The answer to the question is "No, DO-178 does not specifically require Static Analysis for any DAL level."
What I answered, was where Static Analysis fell in, under DO-178 were you to include it. The Software Development Plan (SDP) or Software Verification Plan (SVP), and why it's included. Now the question of whether you can get a DER and AER to sign off on a PSAC/SDP/SVP that are for DAL A software and don't include Static Analysis is a separate issue, but there'd likely need to be a good amount of justification why it's not being used.

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text:
What is the difference between a navigation database and an airport mapping database?
What is the difference between "navigation database" and "airport mapping database"? Are those both required by flight management software for flight planning?

Where are you seeing these terms?

Particularly the second term, since a navigation database would include airports and airport layout.

Navigation databases are typically targeted at FMS based systems, usually using the ARINC-424 standard.  These are ASCII database files that describe aspects such as approach procedures, flight plans, spacing, etc.  It would also provide basic runway information such as heading and altitude of touchdown points - enough to navigate but not enough to paint a completely pretty picture.
By contrast Airport Mapping Databases provide a detailed layout of the entire airport in question - runways, taxiways, vertical structures such as buildings, etc.  The industry standard is ARINC-816 for the databases themselves, but the content is based on DO-272's parameters.  They are usually installed into systems with displays, e.g. Electronic Flight Bags (EFBs) - this may include Class 2 EFBs that are simply iPads for ground-only operation.
Moving maps of this type provide situational awareness, especially when coupled with Cockpit Display of Traffic Information (CDTI) and its associated applications utilizing ADS-B/TIS-B: these provide awareness as to other aircraft that might be in the vicinity, threat level, etc.
Side note: additional CDTI applications that utilize ADS-B are enumerated in DO-317.  These include airborne procedures, e.g. decreased spacing for in-trail procedures (ITP).

Moving maps while taxiing are not unusual these days.

Moving maps while taxiing are quite normal today.

@Terrance you have given a good answer and I upvoted it. i took out my comment as it was redundant.

Makes me mad when the OP abandons their question.


text:
Do regulations require electronic checklists to be displayed on a cockpit screen or EFB?
As per regulation is it required to have the checklist (Normal and Emergency (drive by any alert))  as a part of the Cockpit Display System or EFB?

I’m not sure what you’re asking here. Practically speaking, where else would an electronic checklist be displayed? Or are you simply asking if electronic checklists are required by regulation?

Related, at least for US regulations

No, nothing in the CFRs requires an electronic checklist.  In fact, almost the reverse is true - from experience I know that part 135 operators need to justify the use of EFBs, and have it approved on their operating certificate.  (i.e. FAA doesn't force them, they must demonstrate that the devices meet applicable standards and basically ask for permission...)
And I don't know of any GA aircraft that have electronic checklists built into their displays, although I cannot say that the capability doesn't exist.
Although many airline and GA pilots fly with EFBs, a great many do not.  It would be a tremendous burden to owners and pilots, and a regulatory nightmare to attempt to enforce the use of electronic checklists.
And there is absolutely no compelling reason to do so... The battery will never run out on a laminated paper checklist, so why would you want to force someone to use a less reliable method?

FWIW, most of the newer Garmin PFDs have checklists built in. The C172S G1000 has them, for example, and that's been around since 2006. I assume the same is true for other manufacturers. There's some evidence - or at least some plausible arguments - that they're preferable to paper.

Part 121 matches your experience -- while we have the checklists (both normal and QRH) on our EFB, we're required to use the paper version during operations.  You can study the electronic version of the QRH, and of course the search/find capability is better on the e-reader, but paper is what we're required to use.  (Of course, the 777 with EICAS & the checklist integrated into the aircraft software is a different story.)

@Ralph J, thanks for the concurrence.  I am on day three of Part 121 ground school!

Congrats!!! Very cool!


text:
What is the difference between ACARS and ADS-B?
What is the difference between ACARS and ADS-B?
For weather information in-flight or pre-flight which one is used?

They're two separate protocols. ADS-B is used for transponder reporting and TCAS; ACARS is for relaying information from the company (airline) to pilots.

Are you referring to FIS-B, rather than ADS-B?

You may add your current understanding of both systems so that we can adapt the answer to address the points unclear to you.


text:
Why does a Thrust Vector Control System increase maneuverability?
So why can a thrust vector control system increase my maximum g-load capacity? Because still n=L/G is relevant and if I can not provide enough lift (pointing up) to counter balance the thrust (pointing down to spin a missile around c.g.), why should I use it?

Because sometimes you just desperately want to turn, e.g to get out of a spin or stall, regardless of how much lift is available.

" . . . my maximum g-load capacity?' refers to you as an individual, or the airplane?

Your question isn't very clear.  i.e. "why should I use it?"  Are you designing a missile for a class project, or flying combat simulator games and wondering how to be more effective in defending against them?

It looks like you have created multiple accounts. Be aware that you won't be able to fully participate to the site if you don't gather enough reputation. It is easier to do so by having one single registered account: https://aviation.stackexchange.com/help/merging-accounts

The point of thrust vector control is post-stall maneuvering.
Control surfaces lose much of their effectiveness when the flow over them is separated. Pointing the jet exhaust in different directions works almost regardless of angle of attack. All that is required is good intake flow, and by placing the intake below the forebody (as done on the X-31, the F-16 or the EF-2000), this is still possible even at high angles of attack.
Post-stall maneuvering enables the airplane to point its sensors and weapons in the direction of an opponent within seconds of detection. Compare that to flying a turn at Mach 0.8 over maybe 150°. At 6g (= 80° bank angle), this takes 11.5 seconds, assuming a speed of 256 m/s (which is Mach 0.8 at medium altitude) and an instantly achieved maximum turn rate.
By attaining a very high angle of attack in order to slow down the airplane and thrust vector controlled rotation of the fuselage into the direction of the opponent (Herbst maneuver), an airplane can turn much quicker and, consequently, shoot earlier. This is critical for winning in air-to-air combat.

A max G limit is generally imposed due to the load the wing is capable of.  Specifically, the bending moment it can sustain.
Think about it, in a hard turn the wing and fuselage experience forces in opposite directions:  The wing is creating lift in the direction of the turn, while "centrifugal force" wants to sling the fuselage to the outside of the turn.  This makes the wing bend.
However, in the same turn if you had a thrust nozzle that could generate thrust acting on the fuselage towards the inside of the turn you would reduce that bending stress on the wing, increasing the margin for G available.
ADDENDUM:
While I think my explanation is useful, (based on my interpretation of the question) it is highly unlikely that a VTOL type jet would use this technique at high speed to counter the risk of structural overstress.  Rather, aircraft like the Harrier can use this to its advantage when maneuvering at lower speeds to reduce the risk of an accelerated stall.

Most aircraft with TVC actually deflect thrust upwards to increase turn rate, as they are mainly trying to do nose-up maneuvers to bring their weapons and sensors to bear. Aircraft that can use their thrust to aid the wing in creating lift are just VTOLs. Harriers did VIFFing (vectoring in forward flight) ostensibly to push the opposing Mirages and Etendards to fly slower, where they are not optimized to maneuver, and beat them in dogfights. Even for the Harrier, VIFFing does not necessarily increase turn rate, but it helps push the enemy aircraft to fly way slower than their optimum.

@Efe Balli, I will admit that I am not well versed in combat tactics of thrust vectoring aircraft, but your first sentence about deflecting thrust upwards to increase turn rate would only be applicable in a negative G turn.  Most fighters have much more positive G available, and it is far more comfortable on the pilot to stay positive.  Unless I am missing something...

They deflect thrust upwards to create more nose-up pitching moment, it is not directly related to creating more lift. It reduces net lift as the thrust is negating some lift, but the point is just to keep the aircraft in control post-stall (as in the first answer) or to turn the aircraft further, to bring the guns to bear. In other words, TVC for frontline fighters does not serve to augment max-G turning, it is mainly for slow speed, post-stall control.

Ok, I get it.  You meant tailpipe thrust deflected upwards to pivot the nose.  I had in my mind something forward of the CG, like a Harrier...  This highlights that the question isn't really clear, and my answer might not be appropriate to what they are asking.

TVC of frontline fighters (which the Harrier is not) works this way, they use actuators on the nozzle for that purpose. The F-35B, the only other VTOL fighter, to my knowledge cannot use the rear nozzle or the LiftFan in maneuvering flight.

Yes, I am old school, and am more familiar with the Harriers in use by the USMC while I was active duty than modern adjustable tail nozzle fighters.  But I understand how they work.

Let us continue this discussion in chat.


text:
GNS 480 - OBS resolver calibration fails
Question about VOR/OBS use with a GPS...
I'm installing a GNS 480 in my Cessna 150. I'm retaining the Bendix King KI-209A CDI in the plane.
I've got the resolver plumbed back to the GPS, but when I set up the resolver in the GPS, it says "Calibration Failed." Interestingly, on that same screen, it shows the OBS heading from the CDI. (More on that below)
I've confirmed on that the SIN/COS signals are getting back to the GPS. I'm not swearing that they are within spec, but they look at least reasonable on the oscilloscope.
The Garmin manual states: "The OBS resolver should be compatible with a standard 6-wire OBS interface...Any electrical zero crossing will work because the GNS 480 will calibrate out any errors." The CDI appears to cross zero at 45 degrees, according to both the GPS and the Bendix King manual.
FWIW, the 209A uses a single wire for the ground wire for all three signals: exciter, SIN and COS. I've spliced that into three separate wires at the CDI end, with each pair in a shielded, twisted pair cable.
Of the many trials I made with the Resolver Calibration page, one time the "Current Resolver Value" changed as I turned the OBS in the CDI. I tried to recreate that behavior another dozen times, with no success. Every other time, it will show the a value that changed proportionally with a recent OBS setting...but does not change as a turn the OBS.
Also notable, I mapped out every 30 degrees setting, the GPS reads 0 at CDI 45 and changes linearly...except that it turns the opposite way.
If you've read this far, your probably nerdy enough to appreciate this video, showing most of what I've described here:

Any suggestions?

There are a number of reasons why most avionics installers hate synchros/resolvers with a passion. They are one of the earliest of the common analog interfaces and pretty much every manufacturer did their own thing. Eventually ARINC got around to addressing the subject, but there was no real standardization due to the large number of existing installations. If you do get a copy of ARINC 407-1 Synchro Systems Manual, it give a good explanation of theory. But with the lack of standards, the summary basically reads: When it works, you got it right.
So to your problem: You have three 2-wire circuits; sin, cos, and ref/excitation. Any one of them may be inverted signal/ground. Try swapping the two wires. An inverted ref can cause the OBS to rotate the wrong direction. If N and S are correct, but E and W are reversed, the sin signal is inverted. Similarly, if E and W are correct, but N and S are reversed, the cos is inverted. It's also possible the sin and cos signals are 'mislabeled'. It's not too common with resolvers but it does happen regularly with x, y, z synchros. The best advice from my experience is work through the combinations until it works.
One thing, I'm not familiar with is the GNS480 auto calibration logic. My primary concern is making sure each new configuration restarts the cal from the beginning. It may be worth a call to Garmin tech support.


text:
Are there exceptions to the expiration of an aircraft registration?
I’m currently a working CFI, and encountered an interesting scenario with one of my students recently. While discussing aircraft registration (specifically expiration,) I pulled out the registration card from an aircraft in our fleet. The card looked similar to this:
Which looks normal. However, this example is exactly the situation I encountered. It appears this registration is valid for six years, as opposed to three. I’ve never heard of a registration being valid for six years, and can find no FAR reference to support the six year registration. 47.40 turns up nothing. Additionally, the ole’ Google search turns up nothing.
Does anyone know where I could find the regulatory reference for this?

Note that registration was just retroactively changed to seven years.


text:
Do propeller coefficients go to zero at the same value of advance ratio?
Graphs of power coefficient ($C_P$), thrust coefficient ($C_T$), and efficiency ($\eta=JC_T/C_P$) of the 5868-R6 propeller as functions of advance ratio ($J=V/(nD)$) and propeller pitch (blade angle at 0.75R?) are found in many textbooks (such as McCormic):

From these curves it seems that for a given propeller pitch $C_P$, $C_T$, and $\eta$ go to zero at the same value of $J$. At also seems that the slopes of the $C_T$ vs $J$ curves for higher value of $J$ (where $C_T$ approaches zero) are the same.
I have two questions:

Do $C_P$, $C_T$, and $\eta$ always go to zero simultaneously at the
same value of $J$ for all propellers?  Why?
Are the slopes of the $C_T$ vs $J$ curves where
$C_T\rightarrow 0$ the same for all values of propeller pitch?

If $C_T$ is 0, then by the definition of $\eta=JC_T/C_P$, $\eta=0$, irrespective of the value of $J$.

Yes @ROIMaison, that answers one part of the first question.  If $C_T=0$ at $J=J_0$, then $\eta=0$ at $0$ and at $J_0$.  :-)

Do $C_P$, $C_T$, and $\eta$ always go to zero simultaneously at the
    same value of $J$ for all propellers?  Why?
Yes; Talking in dimensional quantities, This speed, at which all coefficients goes to zero is called pitch speed.
At pitch speed thrust goes to zero due to the fact that the incoming airflow drives the apparent angle of attack seen by the blades to zero.
Power = Thrust * velocity , As thrust goes to zero power goes to zero as well.
Efficiency $\eta = \frac{P_{out}}{P_{in}}$, $P_{out}$ goes to zero as shown above hence $\eta$ goes to zero.
HTH

Thank you for the answer to the first part of my question, @ABCD.  Any thoughts on the second part?

Hi @Christo, sorry Im not clear what do you mean by the second part. Ct will always be some finite value. it doesnt go to infinity

Sorry, @ABCD!  It was a typo; I edited the question.  It should be the slope of CT vs J as CT decreases to zero.

HI @Christo, Not really, the slope depends on the pitch/diameter ratio. You can see this trend in your second image attached. The reason is for a given RPM and diameter, higher pitch propeller has higher pitch speed and hence shallower slope. HTH

Does a negative power coefficient have any meaning? I.e. can the curves be said to  "continue" below the X axis in any meaningful sense? Asking because in the configuration tables for Microsoft Flight simulator engine and propeller combinations, the table that gives the power coefficient values for different advance ratios and propeller pitch angles, the power coefficient is negative for high J values.


text:
Can aircraft ferry engines for other types of aircraft?
There have been a number of questions that highlighted the fact that the 747 could ferry an engine on an underwing pod.
Was the 747 only capable of ferrying 747 engines? Or was it possible to ferry engines for other types of aircraft?
If it can only ferry 747 engines, is there, or has there ever been, an aircraft that can, and has, ferried engines of other aircraft types?
Edit: Following the comments and the one answer posted to date - ideally, I'm looking for cases of aircraft that can ferry engines externally for other types of aircraft. However, if no such case exists (and I suspect this to be the case), it would be nice to see more comprehensive details of how engines are ferried around the world (I'm sure i.e. Qantas won't always  use sea cargo, nor an An-124 to)

Maybe not, because the Virgin Orbit 747's hardpoint was "extensively modified" to carry the LauncherOne rocket.  So adapting the hardpoint to other engines might just cost too much, compared to what else the engineers might work on.  Photos I found of 707s and DC-8s and TriStars ferrying showed them only carrying their own kind of engine.

Would this answer your question?

@PeterKämpf I think at best it's only a partial answer - that skymonster is custom built as opposed to a standard aircraft with this curious feature.

Raytheon regularly straps different engines to its 747 as part of a testing program. An appropriate search is "engine test bed aircraft", you'll get numerous examples. Note, this isn't specific to ferrying (although it could be used for that), these are mainly test platforms.

@RonBeyer Interesting yes, but it's a modification to replace an engine for testing purposes. However, they're not ferrying the engine. There are plenty of photos of commercial flights ferrying an engine, but I'm curious to know whether it's possible to ferry an engine for a different type of aircraft.

We used to haul engines all the time in the C-130.  If you want to limit this to mounting it externally then you should specify that.

What sort of engines?  At the lower end, I would imagine that Lycoming & Continental engines get shipped by air freight fairly often.  From there up, why would shipping engines be any different from shipping any other freight?  As long as it fits in the cargo bay, why not?

https://aviation.stackexchange.com/questions/24181/can-the-a380-ferry-an-extra-engine-like-the-747

@Holmez You did note that the answer also says that most engines fit inside the 747, didn't you?

@PeterKämpf I did notice that. I guess the answer is going to be that most smaller engines can be ferried as internally carried cargo, and that certain types of aircraft, such as the 747, can ferry engines of their own type on underwing pods.How about ferrying of 777 or 380 engines? Can they be carried as internal cargo?

Yes

Yes.
The Antonov 124 regularly ferries even the largest engine, the GE9X, internally. Нема проблем!

GE9X being loaded into the An-124 (picture source)


text:
What aerodynamic implications would a fictional two-pronged fuselage have?
Often I see some fictional futuristic aircraft with a two-pronged fuselage, as if they were absurdly oversized canards.
Is there any remote possibility for an aircraft to benefit from such a design?
What would the implications of it be in an actual aircraft?
picture merely demonstrative

Image source: Vic Viper, You are Cleared for Take-Off—kotaku.com

EDIT: Just to clarify things up a little, since I kind of came out of nowhere asking this weirdness.
  These forked-wing designs is notoriously an aesthetic artifact, my intention is to design a handful of fictional aircraft for a hard-sci-fi novel. I find this design very beautiful but it just screams out impracticity, since I don't like the idea of designing something that wouldn't even take off, i'm after thoughts from specialists and enthusiasts about such design, to seek for any feasible excuses to use it, if it does not gives any positive point except for looking nice, i may just scrap it and get going with more rational designs.

Looks like a Vic Viper T301 and an X-29 had a baby.

The space shuttle has been recycled?

Related: http://aviation.stackexchange.com/q/12963/69

This is actually something that has been investigated, at least in some dimension; one prototype aircraft, the XF5F, had one long wing with the leading edge some distance forward of the pilot. The purpose of this prototype was to examine an aircraft with exceptionally high rate of climb, achieved by the two large engines - uncharacteristic for an aircraft so small. The position of the engines means that the centre of gravity is quite far forwards; the wing being in front of the cockpit counters this somewhat by bringing the centre of lift further forwards too.
The prototype apparently performed well and was loved by its test pilots (though some of this can be put down to its innovative contra-rotating propellers, a new development at the time). It was soon replaced with a much altered and more conventional version, so never saw any real action.
Anyway, the point I'm trying to make here is that in Layman's terms, I believe the only reason for canards or wings projecting so far in front of the cockpit would be to counter something which brought the aircraft's mass unusually far forwards. Even then, I see little reason for splitting this wing into 2 segments to give your pronged design - maybe to give the pilot a better view?
Edit: In response to Lucas Flicky's edit, I'll add a thought on how/why this might be practical in a sci-fi setting.
As I've said, we need a reason for the CoM to be further forward, necessitating a lifting body at the front of the fuselage. There are a couple of ideas I can think of - one of which is weaponry. Stick some big, heavy guns on the ends of your forward wings and they'll effectively balance out the cockpit at the rear of the aircraft. A good excuse for this would be dangerous lateral discharge when the weapon is fired - you simply can't have them behind the cockpit on conventional wings, as this would endanger the pilot. And as I said earlier, you can split the canards in the middle to give the pilot a more commanding view.
As a side note - this seems like an impractical design as it means you can't fly any unarmed versions of the same aircraft. In fact a similar issue very nearly existed with the Eurofighter - the RAF very nearly introduced a policy disallowing the use of guns on the aircraft. Had this rule remained in place (it was overturned in 2006), the Typhoon would have been delivered with their cannons installed but disarmed, as they were required for ballast!

Interesting.  Suppose you combined that with a P-38, by moving the pilot's pod back a bit?

@jamesqf Yes, absolutely. In fact, the pilot in the P-38 is already seated quite far back - just about in line with the leading edge of the wings. In this case it's the weight of the armament in the nose that counters the weight of the cockpit.

this detail about having a heavier back and need protruded wings to balance it out is a really nice thing to have in mind.  plus  the fact that would be an attack exclusive model due to low maneuverability and mandatory possession of weapons.

@LucasFlicky Careful, it sounds like you're perhaps misinterpreting my explanation? Wings generate lift, which counters mass. Wings situated at the front will counter weight at the front; wings nearer the back would be necessary to counter weight at the back. It's a delicate see-saw of forces!

oh, i get it. i indeed misinterpreted a part. so the lift must be applied in the same spot the extra weight is being carried.

That's it, yes. Think of the wings being the centre pivot of the see-saw!

This also explains why flying-wing planes has the optimal lift x drag balance, since there's no fuselage body at all

As far as canards are concerned, I believe the true purpose is to prevent an unrecoverable stall. They are normally set a few degrees higher than the wing so that they stall before the wing does. When the canard stalls, the nose drops, the aircraft picks up airspeed, increasing lift and returning the aircraft to stable flight.

@LuftBier Quite right, but as a side effect of this it allows more aircraft mass to be placed further forwards. The nose wouldn't pitch down when the canards stalled if the centre of gravity wasn't in front of the wing roots.

I don't see any benefit (besides optics, but this is debatable). Compared to a single fuselage, these disadvantages exist:

More wetted surface for the same volume, so more friction drag.
Twin fuselages will obstruct the pilot's view more than one.
The two-pronged fuselage has a higher roll inertia, so it reduces agility.
Any instrumentation will be blocked at the side of the other fuselage, so you need more complex sensors and a sensor fusion algorithm.
The wake from the fuselage will affect the wing more than that of a single fuselage. One consequence will be lower maximum lift of the wing. This is compensated by forebody lift, but this lift is created in a very inefficient way.

Also, the fin in the picture is too small to provide sufficient directional stability without artificial enhancement.

One could compare this design to the F-35 Lightning II; specifically, the engine placement on the F-35. As you can see in the image below, the engine is placed unusually far to the front, and as a result, the tailplane is very similar to the situation you describe - only in reverse.
The reason for this is (amongst others) radar cross-section. Since the engine has a terrible radar cross-section (lots of rotating parts that will reflect radiation everywhere), it is placed in a more 'hidden' spot, nicely between the tailplane. Although this did cause some problems with placing the landing gear, increased weight due to the odd tail assembly, and a generally 'fatter' airplane, this was evidently worth it.
Similarly, a cockpit contains many reflective parts. Especially in a science fiction setting, one could easily conceive of a scenario where simply applying a special coating to the cockpit is insufficient to mask the cockpit internals from RADAR (or other more futuristic detection methods). Placing the cockpit further aft, nicely hidden between the canard wings, could be a viable method of reducing the radar cross-section.

Taken from Why is the F-35 engine nozzle exposed?

You could motivate an aircraft featuring a twin fuselage with benefits in the engine intake characteristic. Fighter aircraft with engine intakes mounted on the side of the fuselage suffer from high yaw angles/rotations due to turbulences from the fuselage. Similar effects occur with underbelly intakes at negative pitch. Protruding fuselages may be designed with center air intakes and thus allow good engine performance over a wide range for aircraft angles and rotation.
There are plenty of reasons against this twin-fuselage design (with many of them in fact being posted in this thread). That should not hinder you from justifying your design trade-off with a proper explanation.


text:
Is there a light civilian helicopter capable of a 250 NM trip without refueling?
Is there any light civilian (GA) helicopter that's capable of making a 250 NM trip with required fuel reserves? I'm thinking of something smaller and lighter that a private individual might buy. (I'm thinking about something that costs less than USD 150K, if that helps to explain the type/size of helicopter I'm asking about.)
The Robinson R22 and RotorWay A600 look like they wouldn't make it without a refueling stop, and I haven't found any extended range STCs for these either.
Does anyone know if such a helicopter exists?

I'm voting to close this question as off-topic because I don't believe we entertain shopping recommendations on Aviation.SE any more than we do on any other Stack...

Helicopter under $150k? Maybe one that is close to timing out... Be aware that the very expensive parts (like gear boxes) on heli's have a limited lifespan. For example, the R-22 requires a very expensive major overhaul at 2200 hours or 12 years involving rotor systems, drive system, control system, and fuselage.

Fail to see how "is there a G.A. helicoptor out there with 250NM range" is off topic.  The O.P. mentions his motivation for asking, but the question is either on-topic or not, irrespective of the motivation behind it.

@RalphJ Help center cites the following as off topic: Resource location: Where to buy a specific part, "Which headset is the best?", etc. This question sounds very much like a resource location question which would fit well elsewhere but not here.

This question is neither "where to buy" nor asking for opinions on "best". The 250NM range question is purely factual, and entirely on-topic.

@RalphJ yes, but the "under $150k" is not.

Sounds like a job for a cessna 152 and a cheap airport car at your destination.

@acpilot Yeah, that's option #2 :) Though, having a heli as a time-builder would be pretty awesome and just so happens that I have family at 250nm in ether direction...

Thanks to those who edited the question rather than just closing it! I really appreciate it

Given the means I'd likely go for the heli.  You only live once so why not do it right??!!

It would seem your budget and desired range are at odds with each other. Someone linked this on another question: https://en.wikipedia.org/wiki/List_of_ultralight_helicopters - There are several in that list that start at $140k-150k, but range is usually < 200nm.

I would need a definition of the word 'light' as it is a little relative.  Most light turbine helicopters eg a Bell 206 JetRanger or a Hughes 500 will do this job just fine.
It is a little difficult to locate a reciprocating engine powered helo that meets those criteria.  The Guimbal Cabri G2 and the Robinson R44 would be my choices for that but cost over $300,000 a piece.
The Schweizer (now Sikorsky) S333 would be another good choice.  It is a light turbine helicopter and can be obtained for just shy of 200,000 USD, though you may be required to put another 100,000 USD or so into it.


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Is an ultralight aircraft allowed to fly near Class B airspace?
May an ultralight vehicle operating under FAR part 103 operate within Class G and E airspace while within the mode C veil surrounding a Class B airport?
Quoting directly from Title 14 CFR 91.1 Applicability

FAR 91.1(e) This part does not apply to any aircraft or vehicle governed by part 103 of this chapter, or subparts B, C, or D of part 101 of this chapter.

Part 103 addresses airspace in this way
103.17 Operations in certain airspace

No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.

Where can I find a restriction that applies to ultralight operation within the mode C veil but still in Class E or G airspace?

It looks like you've already found the relevant regulations, what are you unsure about? Part 91 doesn't apply to ultralights.

Yes, an ultralight aircraft operated under 14 CFR 103 can be operated within the "Mode C Veil" within the limitations of §103.
As you note, 14 CFR 91—including §91.215, ATC transponder and altitude reporting equipment and use—does not apply to ultralights governed by §103.
The limitations of §103 do generally prohibit: operations over congested areas; operations in certain types of airspace; operations in certain types of airspace.

§103.15   Operations over congested areas.
No person may operate an ultralight vehicle over any congested area of a city, town, or settlement, or over any open air assembly of persons.

§103.17   Operations in certain airspace.
  No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.

§103.19   Operations in prohibited or restricted areas.
  No person may operate an ultralight vehicle in prohibited or restricted areas unless that person has permission from the using or controlling agency, as appropriate.

Let's look at an example, the MSP Class B area:

Point A, near A R S Sports Strip (7Y7), would be an area where operations under §103 would be allowable. It is not a congested area, and is not a type of airspace for which operations under §103 are prohibited.
Points B, C, and D, however, would be areas where operations under §103 are generally prohibited. Point B is arguably over congested areas, and by that determination would therefore be prohibited under §103.15. Points C and D are in Class D and B airspace, respectively, and are therefore prohibited under §103.17. The exception would be where the operation has received prior authorization as specified in §103.17 above.
For what it is worth, I have personally witnessed ultralight type aircraft flying in the area of Point A.

You can fly through the mode C Veil but you need to contact the control facility first. I would consider no transponder the same as an inoperative one.

For flying into a Mode C veil without an operable transponder, the
  pilot needs to telephone the appropriate radar facility for the Class
  B airspace and ask for permission to make the flight. Upon agreeing to
  conditions (including direction of flight and altitude), the pilot
  will be given a code number that he will mention to the controller
  upon initial radio contact. This is the same procedure that a pilot
  with an inoperative transponder/encoder would use to fly in or out of
  the Mode C-veil airports for avionics repair.

You were previously allowed to operate in the Veil with out a transponder but the FAA has since changed its ruling on that.

The FAA on January 13 withdrew the "Mode C Veil Exemption" (SFAR No.
  62), which permits aircraft without altitude encoding transponders to
  operate out of specified satellite airports within 30 nm of a Class B
  airspace primary airport. It's not yet known if the FAA is going to
  start immediately enforcing the provisions of FAR 91.215, requiring
  all electrically equipped aircraft to have Mode C transponders when
  operating within a Mode C veil.

You can find more here.
Since the question has been expanded a bit ill add to my answer. Keep in mind im no lawyer and this is simply my advice. Your best bet for this one is to call your local FSDO and get an official answer from the FAA. Since 103 does not explicitly cover this case, in reality if you were to be in breach of it (or the FAA thinks you are) they may reference the precedent set by part 91 on the matter even though there is no explicit rule in part 103.

None of the material cited in this answer applies to operations governed by §103. Apart from that fact, this would be a good answer concerning operations governed by  §91.

There is no explicit ruling in FAR 103 on the matter as there is in 91. In practice the FAA can and may very well use the precedent set in other regulations (91) to make a ruling should an infraction occur.

That is simply not how FAA regulations work; defined applicability and term definitions exist for a reason. If what you suggest were true, UAS systems under §107, and moored balloons, kites, amateur rockets, and hobby model aircraft under §101 might all be required to have transponders or otherwise have exemptions for operation in the "mode C veil". Innumerable other "precedents" would come into play wreaking havoc on the otherwise carefully laid out aviation regulations. This is simply not the case. As is clearly defined, §91 is not governed by §135, and §103 is not governed by 91, etc.

Im implying that this is how the US legal system works, not how the FAA regulations work. I am not saying that all part 91 regulations apply elsewhere but in the event of an infraction and case hearing (if they chose to go that far) they can use other precedent to come to a ruling on the matter.

There is no infraction when no regulation  is broken.

Let's make it simple if your ultra light does not have an electrical system like an alternator or generator you did not have to have a transponder. If you're flying into a mode C Veil The only reason why there is a mode C Veil is because there's going to be a class Bravo airport in the middle of it.
Obviously you have to stay out of class Bravo airspace. One of the examples previous to my post there was a listing for Zone B and Zone C, you could fly in that area as long as you remained under the class Bravo Shelf! You might be flying under part 103 but the rules of far 91 and 61 still apply to you.
If you're flying under part 103 which means you're doing a VFR flight that means you do not have to have communications which means obviously you would not be able to call the controller to request a deviation. Nor could you provide any radio discreet code given to you.  You would not need to do that because one you're not answering their class Bravo airspace that they're controlling and two part 91 specifically exempts you from requiring to have a transponder since you have no electrical driven system.
So yes you can fly in the mode C Veil, as long as you stay out of the class Bravo airspace, with no transponder ( as long as you have no electrical system) and you need not call anyone.
Additionally the air map above is not considered a congested area simply because it's yellow. The purpose of the yellow on an air chart is for when you're flying at night to help you identify a congested area that would be illuminated with a lot of lights. It does not necessary mean it's congested and you can't fly above that area for example if you flew above a railroad track going through a major city the railroad track would not be congested with people.

Re "Let's make it simple if your ultra light does not have an electrical system like an alternator or generator you did not have to have a transponder"-- that will change soon, as drones become ever more pervasive.  Hang gliders, paragliders, and sailplanes will undoubtedly be required to have transponders soon.  Many sailplanes carry transponders right now. Btw for more re where ultralights may fly, specifically regarding Class-E-to-surface airspace - https://aviation.stackexchange.com/questions/35297/which-parts-of-class-e-airspace-can-an-ultralight-part-103-fly-in-without-prio/55714#55714

14 CFR 91 does not apply to operations under §103. See 14 CFR 91.1, "Applicability": (e) This part does not apply to any aircraft or vehicle governed by part 103 of this chapter, or subparts B, C, or D of part 101 of this chapter.

The purpose of the yellow area of a sectional chart is to depict "populated" areas. That depiction has nothing specifically to do with luminosity, though there may be a correlation. See the FAA's Aeronautical Chart User Guide: Yellow tinted areas indicate populated places. The FAA's concept of congestion is complex and ill defined. See this question.


text:
Can a propeller with 90° pitching and symmetrical airfoils generate thrust?
Imagine we have a plane that is already moving at a speed $v_{plane}$. At a certain time $t=0$, a motor starts moving a propeller whose blades consist on symmetrical airfoils with $90^\circ$ of pitching (that is, their chords are perfectly parallel to the fuselage of the plane). Under which conditions (if any) would this propeller produce thrust?
Intuitively, one may think that, with $90^\circ$ of pitching, this will just be impossible. Note however that we start from the condition that the airplane is already moving.
Imagine that the rotating speed of the propeller was $\omega_{prop}$. If we analysed the forces generated by a blade in a cross section at radius $R$, they should look like the following (blue for the velocity of air and red for forces produced by the airfoil):

Since the plane is moving and the propeller is rotating, from the perspective of the blade the incoming air will have a nonzero apparent angle of attack. This will produce lift and, if $\frac{c_L}{c_D}$ is sufficiently large, the direction of the resulting force vector ($F_{TOTAL}$ in the diagram) will point slightly to the direction of movement, hence generating thrust.
Is this correct? If so, would a propeller with long blades spinning sufficiently fast generate thrust under these constraints?

The horizontal component of the total aerodynamic force $F_{TOTAL}$ would indeed be a thrust.
Anyway the much bigger vertical component would be the force that had to be won by the torque of the engine. This design wouldn't be efficient: a lot of torque would be needed to produce just a small thrust. This is why real propellers have the airfoils almost perpendicular to your design and rotate with a speed much higher than the speed of flight.

But the AOA would be negative, producing reverse thrust, right?

For how it is drawn in the picture, the AoA is positive since the blade is moving forward ($V_{plane}$) and downward ($\omega_{prop}$). On the opposite side $\omega_{prop}$ would be the other way around so $F_{total}$ would point downward and slightly forward $\rightarrow$ still a lot of torque and few thrust.

Disregard, I was 90 degrees off in my thinking, presuming flat pitch...

@MichaelHall Yes, for blades set at 0 deg pitch (i.e perpendicular to the airflow) the thrust is reversed.  This is how thrust breaking is accomplished with the G-1.


text:
How to determine climb performance for various flight speeds?
I have the following climb performance chart:

and I need to evaluate the maximum rate of climb in different flight conditions.
The problem is, this chart is valid only for 85KIAS. Is there a way to evaluate the maximum rate of climb for other flight speeds, given the RoC and climb gradient @ 85KIAS?
edit: The zero-lift drag coefficient and aspect ratio of the aircraft are given. And it is not important if it is an optimum climb or not, I simply need to predict the maximum achievable rate of climb, given flight speed, altitude and aircraft mass.

Aircraft performance charts all work the same way. Unfortunately, this one only gives the climb speed at 85 knots indicated airspeed (KIAS).
To find the climb speed at different speeds needs more knowledge about the airframe. Then you can apply a simple approximation following this procedure.
The chart does not tell where on the polar the aircraft is. Will it climb better when flying faster or not? This is impossible to tell. Since you have only one speed and one power setting, but a range of masses, the aircraft will not be at its optimum climb setting for most points. We can make an assumption and declare the reference mass of 1700 kg as the point where the cited conditions are at the optimum. But then I would need at least the zero-lift drag and the aspect ratio to make further assumptions.
From the previous answer we take the climb speed equation $$v_z = \frac{v}{C}\cdot sin\gamma = \frac{v}{C}\cdot\frac{T-D}{m\cdot g}$$
and set the correction factor C = 1 for now. The resulting error is small at low speeds. Now we need drag and thrust.
First drag: The drag coefficient $c_D$ is approximately
$$c_D = c_{D0} + \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$$
with the known aspect ratio $AR$ and an assumed Oswald factor $\epsilon$ of 0.85. To arrive from here at the drag we need to multiply this with the dynamic pressure $q = ½\rho\cdot v^2$ and the reference area $S$:
$$D = ½\rho\cdot v^2\cdot S\cdot c_{D0} + \frac{(1700\cdot g)^2}{½\rho\cdot v^2\cdot S\cdot\pi\cdot AR\cdot\epsilon} = ½\rho\cdot v^2\cdot S\cdot c_{D0} + \frac{(1700\cdot g)^2}{½\rho\cdot v^2\cdot\pi\cdot b^2\cdot\epsilon}$$
when we substitute $AR = b^2/S$ with $b$ the span of your airplane. As I said before, induced drag depends on span, not on aspect ratio.
Now for the thrust. In a propeller aircraft power is constant and thrust is inverse with airspeed. Not indicated, but true airspeed, so we need to be careful. At sea level both are equal, and then thrust is straightforward: $$T = \left(½\rho\cdot v_{ref}^2\cdot S\cdot c_{D0} + \frac{(1700\cdot g)^2}{½\rho\cdot v_{ref}^2\cdot\pi\cdot b^2\cdot\epsilon} + \frac{5.5}{v_{ref}}\cdot1700\cdot g\right)\cdot\frac{v_{ref}}{v}$$
with $v_{ref}$ = 43.7278 m/s, which is 85 kts in sane units. The first two terms in the bracket look familiar: They are the drag contribution. The third term accounts for the climb speed of 5.5 m/s at the reference point in sea level altitude, so this accounts for the change in potential energy. If you need the thrust at higher altitudes, please correct $v_{ref}$ with the square root of the density ratio.
If those equations look daunting, continue solving for the climb speed:
$$v_z = \frac{v}{C}\cdot\frac{\left(D + \frac{v_{z_{ref}}}{v_{ref}}\cdot m\cdot g\right)\cdot\frac{v_{ref}}{v} - D}{m\cdot g}$$
$$v_z = \frac{1}{C}\cdot\left(\frac{D\cdot\left(v_{ref}-v\right)}{m\cdot g} + v_{z_{ref}}\right)$$

I edited my question with further details. Thanks.

since that chart comes from a pilot handbook, as a pilot, how would you solve this set of equations in your head while flying/planning the flight?

@Federico: When you are sitting in the plane already, use this analog computer - it will give you the most precise results! Set the conditions and watch the instruments. When planning the flight, finish solving for the climb speed equation.

@Federico As a pilot, using the pilot handbook, you use the information that they give you.  If you want to achieve the listed performance, you climb at the airspeed that they provide.  Assuming that there are no other charts, using anything else essentially makes you a test pilot and you use trial and error to determine the results.  :-)

I believe that the two drag terms in the second last equation are not the same. The first is the "reference drag", that is the drag at V_ref and the second one will be the one at the actual speed. So I am not sure you can simplify the formula like you did.
Anyway, how reliable is the assumption of constant power with airspeed and therefore that thrust is inverse with airspeed? Is it just a theoretical trick or can it be used for actual calculations?


text:
Why is the static margin expressed as percentage of the MAC?
Most textbooks use the static margin (the distance between the aircraft's centre of mass and its aerodynamic centre) to assess the longitudinal static stability.
Instead of using an absolute value for the allowable range of the static margin, it is expressed as a percentage of the Mean Aerodynamic Chord (MAC) - for example between 5 and 30%. Why is this so?
For a given aircraft, the higher its aspect ratio for a given wing area the shorter will the chord become. Hence the MAC will also be smaller. This will in turn reduce the absolute value of the allowable range for the static margin.
Is this simply a convention or is there an aerodynamic or flight mechanics reason why the allowable range for the centre of mass is smaller for smaller MACs or shorter wing chords?

If I say I have a static margin of 1m, does that mean it's a lot or not?

The static margin is the distance between the center of gravity and the neutral point. By itself, this is a dimensional value. This makes it hard to compare between aircraft, so it makes sense to divide it by some other length. That the mean aerodynamic chord has been chosen has several reasons:

The MAC is the reference length for all parameters of longitudinal motion.
The wing's pitching moment scales with the MAC.
The wing's pitch damping changes with the square of the MAC. The biggest contribution to pitch damping, however, is the lever arm of the horizontal tail.

Normally, the tail lever arm is also chosen as a multiple of MAC. A higher wing chord means more tail force is needed in order to set the correct angle of attack. If you compare different airplanes, you will notice that the relative size of the horizontal tail goes down with a higher wing aspect ratio. While GA airplanes have horizontal tails sized to between 20% and 25% of their wing surface, gliders have horizontal tails of around 10% to 15%. It must be said, however, that gliders need less flexibility in their cg location, which is another reason for reducing horizontal tail size.
If all linear dimensions are referenced to MAC and all areas referenced to the wing area, calculations become easier and similarities between different aircraft become obvious.
For lateral motion parameters the usual reference length is the semispan or the span of the wing.

you mention that all linear dimensions should be referenced to the MAC, and all areas should be referenced to the wing area. Does this hold true when analyzing an aircraft with extremely long length and small wing area (e.g. a Zepplin with wings)?

@Geoff: The MAC should be used only for pitch (that's what I meant with longitudinal motion); roll and yaw need a different length (wing span or semispan, depending on local culture). Lighter-than-air vehicles are different again; here it might be hull diameter or hull length, depending on the coefficient.

I'd like to offer a different viewpoint.  The wing's pitch damping contributes little to aircraft pitch damping, so that is not a reason to base the static margin on MAC.  Believe it or not tail size is almost entirely based on trim requirements, not stability, so again basing tail size on wing area or MAC is not important to stability.  Two aircraft can have widely different MAC's, yet have the same actual stability, so comparisons between aircraft using MAC is not really useful nor accurate.  The ONLY reason MAC is referenced for static margin is for convenience for one particular plane only.  If you look at various aircraft (military, commercial, private) you'll find static margins that range from 35% (literally in front of the leading edge - some lear jets) to near 0% for essentially the same flying qualities.  In my (and others) opinion, there is no true relationship between MAC and stability, but I will soon publish a new theory on stability that mostly solves the "how much stability is needed and how do you measure it" problem.  It is interesting that every article/paper I've ever seen (lots of them) shows elaborate stability calculations that conclude nothing more than the CG should be in front of the neutral point - with nothing about how much in front (except the traditional 5-15% MAC).
Hope this peaks your curiosity.


text:
Why do fighters not use thrust burst from under the wings for improved maneuvering?
This is just a postulation upon a few thoughts.
I think it is intuitive to understand that in fighter jets, in a dog-fight scenario, higher turning speed, as in closing the angle between the chasing plane's nose and the tale of the fleeing plane, is beneficial.
One possible solution, I as someone without no knowledge can think of, is bursts of thrust from beneath the wings, which not only helps with turning but, probably with sudden maneuvers?
I am sure that this has a logical reason to avoid since it has not been developed, and I am keen to understand why.

The Harrier was able to do this to an extent using VIFFing. One drawback was that as thrust reduced at higher altitudes, so did the usefulness of VIFFing. (Source: Designed for the Kill by Mike Spick)

"One possible solution, I as someone without no knowledge can think of, is bursts of thrust from beneath the wings", another (after vectored thrust) is to use control canards.

In modern fighter jets maneuvering is less limited by the ability of the aircraft to make the turn but more the pilot's ability to handle the g force.

@TomMcW … as was the case already in WWII. A spitfire couldn't pull as many Gs as the F-16, but without a G-suite the pilot couldn't handle as much either. Cue Pierre Clostermann's anecdote: he chased enemy in a dive, made the kill, but was too close to the sea to pull out, so he pulled the trim, promptly lost consciousness and woke up a few moments later after the plane now pointing almost straight up lost most of its energy. So at high speed, even a spitfire could pull more Gs than the pilot could handle.

Wings are the most efficient known way of creating force perpendicular to the direction of flight. At the cost of relatively little force in the aft direction (the drag) a wing can create a lot of force perpendicularly (the lift, which is tilted to the side to make turn). They do it by using a lot of air as the reaction mass, which is the reason why wings with longer span are more efficient at this.
Therefore simply making the wings larger is more efficient way to turn then adding “lift” engines or turn jets. Because the wing acts as a multiplier of the engine power as long as the side needs to be sideways (from physical point of view this is possible because force perpendicular to the motion path does not do work).
So to make a fighter with good turn rate, they just make the wings larger until

they can't make them strong enough to withstand the force, or
the pilot won't be able to handle the force without fainting anyway.

The later suggests that remotely-piloted vehicles can get significant advantage as their pilots don't feel the forces and cameras and computers can be made to withstand a lot more force than humans. But it will still be done by using large enough wings because that's the most efficient way.

The design of 5th gen fighters makes a lot more sense suddenly! I do see your point about the wings but let's say a chasing plane and a fleeing plane have the same turning rate, what I had in my mind was a sudden increase in that rate for the chasing plane, so that it would have the latter "in sight"?  What you described, as I understand it, is a "generally" better strategy towards improving maneuverability

What's the difference between “burst” and increasing turn rate? To an extent this occurs because higher turn rate does incur higher drag, but in a dogfight, maintaining energy is important, so the pilot has to always think whether tightening the turn is worth the slow down. But there is no specific mechanism that would only give bursts of force, just general mechanisms that have trade-offs. Closest is engine with emergency power that can only be used for two or five minutes before the engine would overheat and fail.

Well, where is this extra underwing burst of thrust going to come from?  You'd have two basic options: A) add some extra engines under the wings with the exhaust nozzles pointed down, B) use the existing engine(s), and run some ducting from the engine to under the wing, with some valves to open and close to control the thrust. Also, getting a very quick "burst" from a engine is difficult, as they have mechanical inertia and take a few seconds to spool up. You get much faster thrust response from an afterburner, so you'll need one of those.
Both of these are going to add a lot of complexity to what is already a very complex system, and most importantly they are going to add a lot of extra weight.  Every extra pound you add the airframe means either less payload (e.g. less missiles), shorter range, or shorter loiter time. So presumably no one has done it because the increased maneuverability is not worth the cost.

Thank you for the answer, would you say that the added weight would actually limit the maneuverability, making the whole process rather impossible, or would it be the "logistical" issues, like the ones you mentioned (e.g. payload restrictions) that would be of concern? cuz when thinking about a small nation requiring air superiority but only in a defensive manner, would not that make sense? to sacrifice, for example, range for better control/maneuverability?

Jan's answer is probably better than mine. Wings are more efficient than engines if you want force perpendicular to the direction of flight.  So yes, you could sacrifice, say, 10% of your range to get more maneuverability by way of adding an engine. But if you just make the wing bigger, you would only have to sacrifice, say, 1% of your range for the same gain in maneuverability.

Actually, this has been done with one military aircraft: the Harrier. Since the Harrier can vector it's thrust nozzles downward for vertical takeoff or landing, it can also move those nozzles downward while in fast forward flight.
The pilot moves the exhaust thrust downward while in forward flight, and the aircraft takes a sudden leap upward. It was used with some effectiveness by the British during the air battles of the Falklands war, when they faced the agile A4 Skyhawks of the Argentine Air Force, flown by expert pilots. As a British pilot ruefully noted after the war - Argentina turns out such good Formula 1 drivers, we should have guessed that they would have very good pilots.
The technique is known as 'viffing', which comes from Vectoring In Flight, I believe.
There is a problem with this technique: it eats airspeed at a high rate.
And, in modern air combat, airspeed is life.
So if you're going to do this, you'd better get your opponent on the first try, or they'll have you at low airspeed and low energy if you miss.


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What was the lift-to-drag ratio for WWI biplanes?
I will be interested to know what was the lift-to-drag ration for a few more known WWI biplanes at take-off, cruise and landing speed; with the propeller running, stopped or non existent (tests in wind tunnels).

It'll be tough to find that unless you rummage around university study archives or find some old NACA reports.  It's easy to give a ballpark figure.  Reasonably clean monoplanes are generally 8:1 to 11:1. A flying barbwire fence like a WW1 biplane would range from 4:1 to 7:1.

@JohnK I'm looking at Wikipedia. Maybe I could infer the value from the specs?

I don't think you could.  You would have to be able to work out the glide angle at different speeds, and so you'd have to have the sink rate at a given speed.

@JohnK well, what i was trying to do was get the thrust/weight then reciprocal. You know, get a lower bound value?

AE Berriman published his respected survey of Aviation in 1913. At that time drag was known as resistance, with other terms such as head resistance or drift also used. He discusses the lift:resistance ratio only with respect to aerofoil design.
It is unlikely that the l/d of the whole aircraft was ever considered quantitavely as a useful number. One might gain some idea by looking at Farnborough wind tunnel results for propeller thrust at given airspeed and RPM, and then comparing those with aircraft fitted with that propeller, but that would have been of little value in a hectic war and would not have been done. Of more use was the relative speeds of different types when given the same engine and propeller, or of a given machine when fitted with a new propeller.
Pilots would have had some idea of how far their machines would glide when the engine failed, as happened often enough, but only hazy notions of actual speeds and sink rates. They would also have struggled with the fact that the gliding speeds and angles for minimum sink rate and maximum distance were different.
With hindsight we can make guesses. Glide slopes remained well below 1:10 until the German soaring gliders of the 1920s. Airspeeds were slow, around 100 mph, so thrust and drag were not as high as might be expected today. While engines had relatively poor power-to-weight, airframes were so light they would sometimes break up under the extreme manoeuvres of combat. A steep gliding angle of say 1:4 would have required an unrealistically powerful engine to generate thrust (nominally) equal to a quarter of the gross weight, so wings were relatively large and lightly-loaded to give better lift at lower speeds.
So I'd hazard that around 1:5 to 1:8 would have been the norm. If anybody knows of a better-researched analysis, I would be delighted to be proved wrong.


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What are the reasons for this radial piston engine shut down procedure?
In a radial piston engine, before the engine is shut down the rpm is brought to a considerable high power setting of approximately 1950 rpm. This is to burn the unburnt carbon in the spark plugs. Are there other reasons for this specific power setting to be selected before the engine shuts down?

What engine are you talking about?  Your statement indicates this is a general procedure with radials, but it's news to me.  I've operated an R-985, and you kill it from idle or just above idle, like any other engine. 1950 rpm is around cruise rpm for a 985.

No Sir, radials do not get run at 1950 RPM before shutdown. That is a higher power setting than a good runup. But it is true that the idle RPM is brought up to around 1000 RPM for a while and the purpose is not to burn the plugs clean -although it couldn't hurt- but to scavenge oil that has pooled in the engine case during idle operation and return it to the oil tank. These engines have a dry sump system where the oil is stored in a reservoir and distributed to the case for lubrication of engine parts, then sucked up by scavenge lines and returned to the oil reservoir. You don't want excess oil sitting in the engine case after shutdown since it can seep into the lower cylinders and cause a hydraulic lock on startup. Source: I operated R-985, R-1340, R-1820, R-1830, R-2600 and R2800's.

It could also be to remove lead deposits from the spark plugs. Some avgas has an agent added to remove lead deposits, this only works above a certain temperature which is achieved above a certain RPM. We had to do a similar procedure in the Cessna 152.

As you will know, Avgas 100LL contains a compound known as Tetra Ethyl
Lead (TEL) which acts as an octane booster for the fuel. This results
in a fuel which is commonly known as a 100 Octane lean mixture and 130
rich mixture Performance Number fuel.
In practice it is even better than this, with ratings more like 106
lean mixture & 130 rich mixture which are far in excess of the
comparable 85 - 87 octane of road fuels. To achieve this a lot of TEL
is used - around 5 times the quantity that was used in the old Leaded
automotive fuels.
This increase in octane allows aviation engines to produce more power
through increased compression ratios or alternatively by increasing
the inlet pressure by using a turbo or a supercharger. The problem
with using Leaded fuels is that they will always burn with more
deposits than unleaded fuels.
The Tetra Ethyl Lead used for octane boost in the fuel naturally
degrades to form Lead Oxide when it is burned. In reality it is this
oxide which gives the octane boost. The problem is that Lead Oxide is
a solid up to about 900 deg C which is well within the wall
temperatures inside a piston engine.
In order to prevent these deposits from forming, a Lead scavenging
compound is added to Avgas 100LL - this compound is Ethylene
Dibromide. This scavenger is designed to react with the Lead oxide to
form Lead Bromide which is more volatile - becoming a gas at around
200 - 250 oC. This is a low enough temperature to ensure that the Lead
is removed from the engine as a gas end it subsequently goes back to
the solid phase as the exhaust gas cools in the atmosphere.
As a point of interest the pale brown / ash coloured staining that is
often seen leading from the exhausts of high powered engines, such as
those found on the warbirds, is in fact Lead Bromide.
To enable this reaction between the Lead Oxide and the scavenger to
work, there needs to be a relatively high combustion temperature.....

Read more at this link.


text:
If an airplane has a Vertical Speed Indicator is there a requirement that it be periodically checked for accuracy?
I believe I understand that there is no specific US FAA requirement for aircraft to carry a Vertical Speed Indicator (VSI).  I believe I understand the basic operation of a VSI.  It measures the rate of change in static pressure experienced by an aircraft and indicates it as altitude change per minute.  And it should indicate zero vertical speed when the aircraft is stationary on the ground.  It's main purpose is to indicate (though usually delayed, if changing) the vertical speed of the aircraft.
I ask this question because I recently flew in a light plane that I believe had an out-of-calibration VSI.  We were only flying around 3000-3500 ft (1000m) MSL so I don't think this was any sort of outlier case.
Suppose the "calibrated leak" in the diaphragm changes (it becomes more 'leaky') so that the instrument still reads zero on the ground, but only indicates (in an extreme case) half the actual vertical speed.  This is quite easily verified in flight by descending at a constant rate for some known amount of time and then comparing that to the altitude change indicated on the altimeter (or better yet, a separate, accurate GPS).  I know that the VSI lags the actual altitude change rate by several seconds, but this was the sanity check I performed after the fact using video shot that included the instrument panel of the aircraft.
How often does it happen where the instrument has lost its ability to accurately indicate the rate of change of altitude?
What amount of error would be considered acceptable?
At least this causes annoyance; at worst it could cause a mishap (e.g. for a pilot trying to set the rate of descent on instrument approach to landing).

VSI are regulated (when mandatory for IFR) by TSO-C8b, AS394A. I don't know the required check frequency, only this can be done on the ground with a Pitot-Static test set. You will find some tolerances at the end of the document. Note there are also IVSI.

@mins - Unfortunately, your linked document could not be opened. Do you have another source for it? Also, since the TSO listed is certifying the part itself, does it also have any regulatory bearing on its use or maintenance?

@DeanF. Unfortunately this is a paying (and expensive) specification for manufacturers, but you may glance at page 101 of this old document for an idea of the content. I really have no more information about the process, just the specs. There is a list of related FAA documents at the end of the manual,you may be able to infer more details from them with a bit of luck.

If you’re not operating under a Minimum Equipment List that requires one, and the typical General Aviation pilot in the USA is not, then “No” is the answer to your posted question. There is no requirement for a VSI under FAR 91.205 hence no specific VSI inspection requirement is stated.
Note that in the USA prior to conducting flight under Instrument Flight Rules, a static pressure system inspection must have been performed within the preceding 24 months (FAR 91.411) and if your VSI is connected to that system, then it would be a part of that inspection but only as a component of the static pressure system.


text:
Is it legal for a deregistered, previously crashed plane to fly?
N4729D, deregistered, just flew over my house.  I saw where it had crashed years earlier; is it legal to fly this plane?

BTW, Welcome to Aviation Stack Exchange.  Aside from not posting in ALL CAPS, you should also take the [tour] and read over the [FAQ] to get a better idea how this site works.

Are registration numbers forever?  That is, if a plane was registered as N4729D and was destroyed, couldn't that number be assigned to another plane?  Indeed, if you owned a plane with a US registration number and moved to say Canada, wouldn't you need to get a Canadian registration?

The word "crashed" says absolutely nothing about the severity of the damage.  Cars crash and are repaired regularly.  As long as questions and concerns about airworthiness are resolved why do you think it would be any different with aircraft?

It isn't legal to fly an aircraft without a valid registration, however if the owner has applied for a new registration then they can fly the aircraft using the application as a temporary registration.
So it's possible that the owner has repaired the aircraft, re-applied for registration, and is now flying the aircraft using the application as temporary authorization.
The general requirement to have a valid registration certificate on board is in 14 CFR 91.203(a) says:

Except as provided in § 91.715, no person may operate a civil aircraft
unless it has within it the following:
[...]
(2) An effective U.S. registration certificate issued to its owner or,
for operation within the United States, the second copy of the
Aircraft registration Application as provided for in § 47.31(c), a
Certificate of Aircraft registration as provided in part 48, or a
registration certification issued under the laws of a foreign country.

According to the FAA's N-number registry, N4729D is indeed deregistered. That doesn't mean it's flying illegally, though. 91.203 mentions 47.31(c), which essentially says that if you've applied for a registration then you can use a copy of the application as a temporary authorization:

After compliance with paragraph (a) of this section, the applicant for
registration of an aircraft last previously registered in the United
States must carry the second copy of the Aircraft Registration
Application in the aircraft as temporary authority to operate without
registration.

This question might be helpful too.


text:
Is it allowed and/or safe to place objects on the dash in a PA28?
I am told by my maintenance engineer that NOTHING is to be put on the dashboard area above the instrument panel - this is where I keep my DUAL GPS to have an unobstructed view of the sky. It was asserted that it could block one of the vacuum vents that are on the top of the dash.
I follow rules to the 'T' but similarly to make up rules 'on the go' is also not appropriate - I could not find a single word about this in the POH?
Can someone tell me if it's allowed and/or safe to place objects there?

What is the question? Our club has the same policy, and it's not in the POH... I've rented PA28's, the school had the same policy, not just for that aircraft, but all of them.

I learned not to put things on the glareshield because it could scratch or wear the windscreen plexiglass. Nothing in the POH, but that doesn’t mean it’s allowed...

Thanks for the comments - the question is, why should you not put a DUAL GPS unit on the coaming panel - are there any technical reasons or is it just to prevent something from scratchin the windscreen , which I fully accept and understand.

Next time you go flying just stick your hand up there and see if you can feel any suction at those holes when the engine is running. I doubt it. The holes in the coaming panel (the flat panel on top of the dash) near the base of the windshield are defroster outlets.
The vacuum pump on the engine accessory case sucks air through the air driven gyros on the instrument panel through rubber hoses interconnected to the vacuum instruments (on the Cherokee there is a regulating valve/manifold between the pump and the instruments).  On the upstream side of the instruments there is an intake hose with a cylindrical filter to filter the cabin air before the pump pulls it through the gyros.
The filter is mounted in the open below the instrument panel somewhere in the jungle of wires and tubes, on a bracket of some kind.  If you slide on your back and get your head under the panel, you should be able to spot a cylinder about the size of a small can of beans with a wire mesh around it and pleats like a car air filter.  That's the vacuum system filter.
The main thing to be wary about when putting electronic devices on top the panel is they may or may not alter the wet compass when turned on.  Better to have an external antenna you can stick there and keep the GPS unit on a control wheel clip or something like that.


text:
When passing a waypoint, when exactly are we on the next leg?
When performing one of the procedures shown in the pictures below, when exactly do we consider ourselves to be on the next leg?
For example: for the fly-by waypoint, when do we consider that we are no longer flying from the runway to Alpha, but we're now on the Alpha to Bravo leg instead? Is it in the middle of the arc, once we finish the arc...? For fly-over waypoints, I guess it's when we pass Alpha, but I'm not sure about that either.

The transition point as defined in RTCA DO-283 RNP MOPS is the point where the aircraft's path passes through a vertical plane that bisects the inbound and outbound legs going through the waypoint.
That generic description covers all the possibilities of the aircraft passing the waypoint regardless of how good or bad it is following the defined path.
Realistically, in the case of the fly-by waypoint, it's the point half way through the transition turn where the waypoint is directly abeam the flight path.
The same rule (crossing the bisecting plane) applied to the fly-over waypoint results in the transition occurring at the waypoint.

I think a diagram would support the explanation, as some people aren't great at turning the verbal description into a geometric description.


text:
How does envelope protection work in Airbus vs. Boeing aircraft?
I keep reading this thing that "On Airbus the computer overrules the pilot, not on Boeing". Smells like urban myth or at least gross oversimplification. How does envelope protection work differently in Airbus and Boeing aircraft?
Boeing: as far as I understand it, it's possible to apply force on the column to override the autopilot and have zero limitations, i.e. you're free to (try to) fly the aircraft in whatever attitude you want.
Airbus: if all the systems are failure-free there's no way to override the autopilot, i.e. you cannot fly in any attitude you want.
Is my understanding/comparison accurate?
It would be really lovely if someone with factual knowledge on the matter elaborate more, maybe explaining the different laws and when they can be / are activated.

Related post What are the main differences piloting Boeing vs. Airbus aircraft? does not answer the question.

Seen, that one, that's where I decided to ask this question. Really on airbus pilots have NO WAY (not even pulling breakers) to supersede the A/P? How is this comment, "On a Boeing, the pilot outranks the auto pilot", sarcastic? I'd like to have a serious, complete, overview of the pilots-a/p relationship on both.

It's not the autopilot which can override the pilot inputs on Airbus aircraft, but the flight envelope protection (laws used in the control computers ELAC, FAC and SEC). The autopilot can be disengaged, the flight envelope is still protected. Related: Is a Control Law Degradation in Airbus Planes displayed on the ECAM?

There is quite a significant difference of envelope protection between the Boeing models. For example, the 737 is quite a different aircraft than the 787. Within the Airbus fleet the differences are less. If you want to prevent oversimplifications and generalisations, perhaps you want to limit the scope of the discussion to certain models.

@DeltaLima While this may be true, you would need to know the answer to this very question do properly limit the scope. This question may be broad in the number of planes it wants to compare, but very specific in what it wants to compare.

I've edited my answer to the other question to improve the use of terminology that might have confused you. Sorry for that.

https://aviation.meta.stackexchange.com/questions/3386/duplicate-lets-be-real-please -Related meta

There are two sorts of "autopilots", and it is important to make a distinction between the two. One is for the behaviour of the aircraft around its Centre of Gravity (CoG), the other one is for defining the path of the CoG.

The Inner Loop autopilot: behaviour around CoG, or the aircraft attitude control. This autopilot should not be called autopilot since its characteristics are actually shielded from the pilot: it does its job without showing what it is doing. It only moves the control surfaces (elevator, ailerons) or helicopter swash plate, and not the flying controls (stick, wheel). To the pilot, the system is invisible and just results in a stable platform, in the case of the A320 and B777 a platform with envelope protection that does not allow for the aeroplane to enter a situation that would be dangerous. In helicopters this system is referred to as Stability Augmentation System (SAS).
The Outer Loop autopilot: defining the path of the CoG, which is ultimately what pilots are paid for :). They are in control of the flight path and administer this control by deflecting the flying controls (stick, pedals). The pilot can delegate this control to a feedback system that provides inputs to the same flying controls, via an actuator with a slip clutch. With an old fashioned mechanical linkage, the actuator moves the whole circuit from stick to surfaces (or swash plate in a helicopter); the pilot can override this input by applying a force greater than the override force of the slip clutch.

So normally, by design, the Outer Loop autopilot shows the pilots what it is doing by moving the flight path input devices for them, in a way that is transparent and can be intuitively overridden by applying a high force. It is this bit where the A320 has a different philosophy: the input stick never moves other than by the hand of the pilot. This main distinguishing feature between the two types of autopilot does not exist in an A320. It does in a B777, which also has an inner loop autopilot plus envelope protection, and an outer loop autopilot which actually does move the column/yoke. So the B777 is functionally identical to the A320 in every meaningful way, plus retains the feature of moving flying controls. It has no mechanical linkage, and it uses two separate sets of actuators for this function: one set for the surfaces, and one for the flying controls.
This is the situation on both Airbus > A320 and Boeing > 777, when all systems are functioning. These aircraft are all dynamically stable: aerodynamics take care of bringing back the aircraft attitude to a neutral position. The F16 for instance is aerodynamically unstable in order to provide high manoeuvrability: it always wants to pitch and roll already, and the flight control computers provide constant rapid inputs to elevators and ailerons to maintain attitude by active control. This is not the case with passenger aircraft, which do not need to be as manoeuvrable as a fighter jet and just need to bring the passengers home safely.
Therefore, both on the Airbuses & Boeings, the aircraft can fly without the Inner Loop autopilots as well, without any problems. The aircraft just lose their envelope protection and now it is possible to command them into potentially dangerous situations such as fully developed stalls. In both types, it is always possible to disconnect the outer loop autopilot. For the inner loop ones:

The B737 does not have one.
In the A320, it is not possible to disconnect the inner loop autopilots if all is functioning correctly, except by pulling circuit breakers for resetting the ELACs as this site indicates;
In the B777 there is a guarded switch that allows disconnection of the envelope protection as @Cpt Reynolds pointed out.

In the latter two types, the system disconnects features by itself if failures are detected, to allow control in degraded mode. Both manufacturers have implemented a direct mode as the lowest mode, where surface deflection is a direct function of stick deflection. There is however no direct mechanical cable connection to the surfaces, even the direct mode is still an electrical input, so technically still Fly By Wire.

Above picture is from Aircraft Systems Mechanical, electrical, and avionics subsystems integration Third Edition Ian Moir Allan Seabridge, and shows the top level comparison of the implementation of the flight control loops. The redundancy features are different, functionality is much the same: both implementations prevent excessive AoA that brings the aircraft into a stall, and excessive bank angle.
So although the functionality of modern Airbuses and Boeings is very similar, we do often see the myth that Airbus ranks the automated systems higher than the pilot. There is a difference in user interface implementation, in that Airbus has sticks that are not coupled with each other, and have no means to be driven other than by hand. At the time of implementation, this was a new feature that pilots were not accustomed to, as was the envelope protection system. New features can be poorly understood by inexperienced users, and the aviation world is conservative: when the DC3 introduced a 3/4 control wheel, pilots were protesting that they might be gripping the bit of the wheel that was missing and that they were used to.
Ultimately, the most relevant fact is that both Airbus and Boeing have excellent and very similar safety numbers, and that both manufacturers make aircraft that enable the pilots to bring the passengers home safely in 99.9999999 % of flights.

best explanation I’ve read in a long time. Another way to explain the two loops is that the inner loop is almost self-contained and does not need any external reference instruments (other than ADIRS) and orders the control surfaces in order to do things like eg: “keep wings level”,  or “keep 5 deg pitch”. Outer loop uses external inputs (pitot,static,navs) and orders to the inner loop in order to do things like “climb 500 fpm” or “turn left hdg 230”

@Radu094 The outer loop usually has its own input mechanism, separate from the stability augmentation system.

I can't help but feel that you have done an excellent job at describing the differences between inner and outer loop control systems ("autopilots"), and how having one isn't necessarily related to having the other; but you haven't really discussed much about flight computer overrides by the pilot, or the differences in how Boeing and Airbus aircraft approach (no pun intended) flight envelope protection, which seems to be the focus of the OP's question, especially as OP is asking for clarification on the oft-quipped "on Airbus the computer overrules the pilot, not on Boeing" (and variants).

Excellent explanation! The only comment I would like to add is that on the 777 there is a guarded switch to take out the „inner loop“ computers completely and render the aircraft, control-wise, a giant equivalent of a Cessna without any meaningful computing in the control loop but with all other functions intact. There is no equivalent of that switch in the A320 - there, it is still possible to disable the inner loop, but it will only be accomplished by sacrificing one aircraft function or another (e.g. some control surfaces will be locked out, or air data computer redundancy will be lost).

THANKYOU!!! This was the answer I was looking for!!! Just please two more things: 1) is it possibile to completely disable even envelope protection by pulling breakers? 2)the presence of the inner loop means that the pilot is always in Fly By Wire mode (i.e. the stick tells the plane the desidered bank angles, not the "surfaces deflection")?

In the B777, there is a guarded switch that disables all envelope protection. In the A320, it is possible to pull breakers and reboot the Flight Augmentation Computers, like what happened in QZ8501. 2) Yes and no:  in the A320 in Normal Law all protections are in place, in Alternate Law (after a failure has been detected) the envelope protections are lost, and in Direct Law the surfaces deflect proportionally to stick input just like a Cessna. But even in Direct Law there is no real mechanical cable connection: still a Wire.

Correction: the QZ8501 pilot reset the FAC using the reset switches in the overhead panel, not the circuit breakers. And the pitch/roll envelope protection is provided by the ELAC, as described in this answer.

This site seems to indicate that there are circuit breakers for the ELACs.

There is another big difference between the inner loops. The Boeing one emulates direct controls within the flight envelope, but for the Airbus one, the side-stick deflection gives desired wing loading and roll rate and the computer calculates the surface position to achieve that. It makes the side-sticks simpler (no force feedback) and normal flying easier (automatic trim), but at the cost of feeling the plane (it won't tend to pitch down if it slows down and up if it accelerates except when it would leave the flight envelope).